Let's get this math done. We have 870 and we're going to multiply it by 423. This is the same as taking 870 and adding it to itself 423 times.
Step 1: 0 + 870 = 870
Step 2: 870 + 870 = 1740
Step 3: 1740 + 870 = 2610
Step 4: 2610 + 870 = 3480
Step 5: 3480 + 870 = 4350
Step 6: 4350 + 870 = 5220
Step 7: 5220 + 870 = 6090
Step 8: 6090 + 870 = 6960
Step 9: 6960 + 870 = 7830
Step 10: 7830 + 870 = 8700
Step 11: 8700 + 870 = 9570
Step 12: 9570 + 870 = 10440
Step 13: 10440 + 870 = 11310
Step 14: 11310 + 870 = 12180
Step 15: 12180 + 870 = 13050
Step 16: 13050 + 870 = 13920
Step 17: 13920 + 870 = 14790
Step 18: 14790 + 870 = 15660
Step 19: 15660 + 870 = 16530
Step 20: 16530 + 870 = 17400
Step 21: 17400 + 870 = 18270
Step 22: 18270 + 870 = 19140
Step 23: 19140 + 870 = 20010
Step 24: 20010 + 870 = 20880
Step 25: 20880 + 870 = 21750
Step 26: 21750 + 870 = 22620
Step 27: 22620 + 870 = 23490
Step 28: 23490 + 870 = 24360
Step 29: 24360 + 870 = 25230
Step 30: 25230 + 870 = 26100
Step 31: 26100 + 870 = 26970
Step 32: 26970 + 870 = 27840
Step 33: 27840 + 870 = 28710
Step 34: 28710 + 870 = 29580
Step 35: 29580 + 870 = 30450
Step 36: 30450 + 870 = 31320
Step 37: 31320 + 870 = 32190
Step 38: 32190 + 870 = 33060
Step 39: 33060 + 870 = 33930
Step 40: 33930 + 870 = 34800
Step 41: 34800 + 870 = 35670
Step 42: 35670 + 870 = 36540
Step 43: 36540 + 870 = 37410
Step 44: 37410 + 870 = 38280
Step 45: 38280 + 870 = 39150
Step 46: 39150 + 870 = 40020
Step 47: 40020 + 870 = 40890
Step 48: 40890 + 870 = 41760
Step 49: 41760 + 870 = 42630
Step 50: 42630 + 870 = 43500
Step 51: 43500 + 870 = 44370
Step 52: 44370 + 870 = 45240
Step 53: 45240 + 870 = 46110
Step 54: 46110 + 870 = 46980
Step 55: 46980 + 870 = 47850
Step 56: 47850 + 870 = 48720
Step 57: 48720 + 870 = 49590
Step 58: 49590 + 870 = 50460
Step 59: 50460 + 870 = 51330
Step 60: 51330 + 870 = 52200
Step 61: 52200 + 870 = 53070
Step 62: 53070 + 870 = 53940
Step 63: 53940 + 870 = 54810
Step 64: 54810 + 870 = 55680
Step 65: 55680 + 870 = 56550
Step 66: 56550 + 870 = 57420
Step 67: 57420 + 870 = 58290
Step 68: 58290 + 870 = 59160
Step 69: 59160 + 870 = 60030
Step 70: 60030 + 870 = 60900
Step 71: 60900 + 870 = 61770
Step 72: 61770 + 870 = 62640
Step 73: 62640 + 870 = 63510
Step 74: 63510 + 870 = 64380
Step 75: 64380 + 870 = 65250
Step 76: 65250 + 870 = 66120
Step 77: 66120 + 870 = 66990
Step 78: 66990 + 870 = 67860
Step 79: 67860 + 870 = 68730
Step 80: 68730 + 870 = 69600
Step 81: 69600 + 870 = 70470
Step 82: 70470 + 870 = 71340
Step 83: 71340 + 870 = 72210
Step 84: 72210 + 870 = 73080
Step 85: 73080 + 870 = 73950
Step 86: 73950 + 870 = 74820
Step 87: 74820 + 870 = 75690
Step 88: 75690 + 870 = 76560
Step 89: 76560 + 870 = 77430
Step 90: 77430 + 870 = 78300
Step 91: 78300 + 870 = 79170
Step 92: 79170 + 870 = 80040
Step 93: 80040 + 870 = 80910
Step 94: 80910 + 870 = 81780
Step 95: 81780 + 870 = 82650
Step 96: 82650 + 870 = 83520
Step 97: 83520 + 870 = 84390
Step 98: 84390 + 870 = 85260
Step 99: 85260 + 870 = 86130
Step 100: 86130 + 870 = 87000
Step 101: 87000 + 870 = 87870
Step 102: 87870 + 870 = 88740
Step 103: 88740 + 870 = 89610
Step 104: 89610 + 870 = 90480
Step 105: 90480 + 870 = 91350
Step 106: 91350 + 870 = 92220
Step 107: 92220 + 870 = 93090
Step 108: 93090 + 870 = 93960
Step 109: 93960 + 870 = 94830
Step 110: 94830 + 870 = 95700
Step 111: 95700 + 870 = 96570
Step 112: 96570 + 870 = 97440
Step 113: 97440 + 870 = 98310
Step 114: 98310 + 870 = 99180
Step 115: 99180 + 870 = 100050
Step 116: 100050 + 870 = 100920
Step 117: 100920 + 870 = 101790
Step 118: 101790 + 870 = 102660
Step 119: 102660 + 870 = 103530
Step 120: 103530 + 870 = 104400
Step 121: 104400 + 870 = 105270
Step 122: 105270 + 870 = 106140
Step 123: 106140 + 870 = 107010
Step 124: 107010 + 870 = 107880
Step 125: 107880 + 870 = 108750
Step 126: 108750 + 870 = 109620
Step 127: 109620 + 870 = 110490
Step 128: 110490 + 870 = 111360
Step 129: 111360 + 870 = 112230
Step 130: 112230 + 870 = 113100
Step 131: 113100 + 870 = 113970
Step 132: 113970 + 870 = 114840
Step 133: 114840 + 870 = 115710
Step 134: 115710 + 870 = 116580
Step 135: 116580 + 870 = 117450
Step 136: 117450 + 870 = 118320
Step 137: 118320 + 870 = 119190
Step 138: 119190 + 870 = 120060
Step 139: 120060 + 870 = 120930
Step 140: 120930 + 870 = 121800
Step 141: 121800 + 870 = 122670
Step 142: 122670 + 870 = 123540
Step 143: 123540 + 870 = 124410
Step 144: 124410 + 870 = 125280
Step 145: 125280 + 870 = 126150
Step 146: 126150 + 870 = 127020
Step 147: 127020 + 870 = 127890
Step 148: 127890 + 870 = 128760
Step 149: 128760 + 870 = 129630
Step 150: 129630 + 870 = 130500
Step 151: 130500 + 870 = 131370
Step 152: 131370 + 870 = 132240
Step 153: 132240 + 870 = 133110
Step 154: 133110 + 870 = 133980
Step 155: 133980 + 870 = 134850
Step 156: 134850 + 870 = 135720
Step 157: 135720 + 870 = 136590
Step 158: 136590 + 870 = 137460
Step 159: 137460 + 870 = 138330
Step 160: 138330 + 870 = 139200
Step 161: 139200 + 870 = 140070
Step 162: 140070 + 870 = 140940
Step 163: 140940 + 870 = 141810
Step 164: 141810 + 870 = 142680
Step 165: 142680 + 870 = 143550
Step 166: 143550 + 870 = 144420
Step 167: 144420 + 870 = 145290
Step 168: 145290 + 870 = 146160
Step 169: 146160 + 870 = 147030
Step 170: 147030 + 870 = 147900
Step 171: 147900 + 870 = 148770
Step 172: 148770 + 870 = 149640
Step 173: 149640 + 870 = 150510
Step 174: 150510 + 870 = 151380
Step 175: 151380 + 870 = 152250
Step 176: 152250 + 870 = 153120
Step 177: 153120 + 870 = 153990
Step 178: 153990 + 870 = 154860
Step 179: 154860 + 870 = 155730
Step 180: 155730 + 870 = 156600
Step 181: 156600 + 870 = 157470
Step 182: 157470 + 870 = 158340
Step 183: 158340 + 870 = 159210
Step 184: 159210 + 870 = 160080
Step 185: 160080 + 870 = 160950
Step 186: 160950 + 870 = 161820
Step 187: 161820 + 870 = 162690
Step 188: 162690 + 870 = 163560
Step 189: 163560 + 870 = 164430
Step 190: 164430 + 870 = 165300
Step 191: 165300 + 870 = 166170
Step 192: 166170 + 870 = 167040
Step 193: 167040 + 870 = 167910
Step 194: 167910 + 870 = 168780
Step 195: 168780 + 870 = 169650
Step 196: 169650 + 870 = 170520
Step 197: 170520 + 870 = 171390
Step 198: 171390 + 870 = 172260
Step 199: 172260 + 870 = 173130
Step 200: 173130 + 870 = 174000
Step 201: 174000 + 870 = 174870
Step 202: 174870 + 870 = 175740
Step 203: 175740 + 870 = 176610
Step 204: 176610 + 870 = 177480
Step 205: 177480 + 870 = 178350
Step 206: 178350 + 870 = 179220
Step 207: 179220 + 870 = 180090
Step 208: 180090 + 870 = 180960
Step 209: 180960 + 870 = 181830
Step 210: 181830 + 870 = 182700
Step 211: 182700 + 870 = 183570
Step 212: 183570 + 870 = 184440
Step 213: 184440 + 870 = 185310
Step 214: 185310 + 870 = 186180
Step 215: 186180 + 870 = 187050
Step 216: 187050 + 870 = 187920
Step 217: 187920 + 870 = 188790
Step 218: 188790 + 870 = 189660
Step 219: 189660 + 870 = 190530
Step 220: 190530 + 870 = 191400
Step 221: 191400 + 870 = 192270
Step 222: 192270 + 870 = 193140
Step 223: 193140 + 870 = 194010
Step 224: 194010 + 870 = 194880
Step 225: 194880 + 870 = 195750
Step 226: 195750 + 870 = 196620
Step 227: 196620 + 870 = 197490
Step 228: 197490 + 870 = 198360
Step 229: 198360 + 870 = 199230
Step 230: 199230 + 870 = 200100
Step 231: 200100 + 870 = 200970
Step 232: 200970 + 870 = 201840
Step 233: 201840 + 870 = 202710
Step 234: 202710 + 870 = 203580
Step 235: 203580 + 870 = 204450
Step 236: 204450 + 870 = 205320
Step 237: 205320 + 870 = 206190
Step 238: 206190 + 870 = 207060
Step 239: 207060 + 870 = 207930
Step 240: 207930 + 870 = 208800
Step 241: 208800 + 870 = 209670
Step 242: 209670 + 870 = 210540
Step 243: 210540 + 870 = 211410
Step 244: 211410 + 870 = 212280
Step 245: 212280 + 870 = 213150
Step 246: 213150 + 870 = 214020
Step 247: 214020 + 870 = 214890
Step 248: 214890 + 870 = 215760
Step 249: 215760 + 870 = 216630
Step 250: 216630 + 870 = 217500
Step 251: 217500 + 870 = 218370
Step 252: 218370 + 870 = 219240
Step 253: 219240 + 870 = 220110
Step 254: 220110 + 870 = 220980
Step 255: 220980 + 870 = 221850
Step 256: 221850 + 870 = 222720
Step 257: 222720 + 870 = 223590
Step 258: 223590 + 870 = 224460
Step 259: 224460 + 870 = 225330
Step 260: 225330 + 870 = 226200
Step 261: 226200 + 870 = 227070
Step 262: 227070 + 870 = 227940
Step 263: 227940 + 870 = 228810
Step 264: 228810 + 870 = 229680
Step 265: 229680 + 870 = 230550
Step 266: 230550 + 870 = 231420
Step 267: 231420 + 870 = 232290
Step 268: 232290 + 870 = 233160
Step 269: 233160 + 870 = 234030
Step 270: 234030 + 870 = 234900
Step 271: 234900 + 870 = 235770
Step 272: 235770 + 870 = 236640
Step 273: 236640 + 870 = 237510
Step 274: 237510 + 870 = 238380
Step 275: 238380 + 870 = 239250
Step 276: 239250 + 870 = 240120
Step 277: 240120 + 870 = 240990
Step 278: 240990 + 870 = 241860
Step 279: 241860 + 870 = 242730
Step 280: 242730 + 870 = 243600
Step 281: 243600 + 870 = 244470
Step 282: 244470 + 870 = 245340
Step 283: 245340 + 870 = 246210
Step 284: 246210 + 870 = 247080
Step 285: 247080 + 870 = 247950
Step 286: 247950 + 870 = 248820
Step 287: 248820 + 870 = 249690
Step 288: 249690 + 870 = 250560
Step 289: 250560 + 870 = 251430
Step 290: 251430 + 870 = 252300
Step 291: 252300 + 870 = 253170
Step 292: 253170 + 870 = 254040
Step 293: 254040 + 870 = 254910
Step 294: 254910 + 870 = 255780
Step 295: 255780 + 870 = 256650
Step 296: 256650 + 870 = 257520
Step 297: 257520 + 870 = 258390
Step 298: 258390 + 870 = 259260
Step 299: 259260 + 870 = 260130
Step 300: 260130 + 870 = 261000
Step 301: 261000 + 870 = 261870
Step 302: 261870 + 870 = 262740
Step 303: 262740 + 870 = 263610
Step 304: 263610 + 870 = 264480
Step 305: 264480 + 870 = 265350
Step 306: 265350 + 870 = 266220
Step 307: 266220 + 870 = 267090
Step 308: 267090 + 870 = 267960
Step 309: 267960 + 870 = 268830
Step 310: 268830 + 870 = 269700
Step 311: 269700 + 870 = 270570
Step 312: 270570 + 870 = 271440
Step 313: 271440 + 870 = 272310
Step 314: 272310 + 870 = 273180
Step 315: 273180 + 870 = 274050
Step 316: 274050 + 870 = 274920
Step 317: 274920 + 870 = 275790
Step 318: 275790 + 870 = 276660
Step 319: 276660 + 870 = 277530
Step 320: 277530 + 870 = 278400
Step 321: 278400 + 870 = 279270
Step 322: 279270 + 870 = 280140
Step 323: 280140 + 870 = 281010
Step 324: 281010 + 870 = 281880
Step 325: 281880 + 870 = 282750
Step 326: 282750 + 870 = 283620
Step 327: 283620 + 870 = 284490
Step 328: 284490 + 870 = 285360
Step 329: 285360 + 870 = 286230
Step 330: 286230 + 870 = 287100
Step 331: 287100 + 870 = 287970
Step 332: 287970 + 870 = 288840
Step 333: 288840 + 870 = 289710
Step 334: 289710 + 870 = 290580
Step 335: 290580 + 870 = 291450
Step 336: 291450 + 870 = 292320
Step 337: 292320 + 870 = 293190
Step 338: 293190 + 870 = 294060
Step 339: 294060 + 870 = 294930
Step 340: 294930 + 870 = 295800
Step 341: 295800 + 870 = 296670
Step 342: 296670 + 870 = 297540
Step 343: 297540 + 870 = 298410
Step 344: 298410 + 870 = 299280
Step 345: 299280 + 870 = 300150
Step 346: 300150 + 870 = 301020
Step 347: 301020 + 870 = 301890
Step 348: 301890 + 870 = 302760
Step 349: 302760 + 870 = 303630
Step 350: 303630 + 870 = 304500
Step 351: 304500 + 870 = 305370
Step 352: 305370 + 870 = 306240
Step 353: 306240 + 870 = 307110
Step 354: 307110 + 870 = 307980
Step 355: 307980 + 870 = 308850
Step 356: 308850 + 870 = 309720
Step 357: 309720 + 870 = 310590
Step 358: 310590 + 870 = 311460
Step 359: 311460 + 870 = 312330
Step 360: 312330 + 870 = 313200
Step 361: 313200 + 870 = 314070
Step 362: 314070 + 870 = 314940
Step 363: 314940 + 870 = 315810
Step 364: 315810 + 870 = 316680
Step 365: 316680 + 870 = 317550
Step 366: 317550 + 870 = 318420
Step 367: 318420 + 870 = 319290
Step 368: 319290 + 870 = 320160
Step 369: 320160 + 870 = 321030
Step 370: 321030 + 870 = 321900
Step 371: 321900 + 870 = 322770
Step 372: 322770 + 870 = 323640
Step 373: 323640 + 870 = 324510
Step 374: 324510 + 870 = 325380
Step 375: 325380 + 870 = 326250
Step 376: 326250 + 870 = 327120
Step 377: 327120 + 870 = 327990
Step 378: 327990 + 870 = 328860
Step 379: 328860 + 870 = 329730
Step 380: 329730 + 870 = 330600
Step 381: 330600 + 870 = 331470
Step 382: 331470 + 870 = 332340
Step 383: 332340 + 870 = 333210
Step 384: 333210 + 870 = 334080
Step 385: 334080 + 870 = 334950
Step 386: 334950 + 870 = 335820
Step 387: 335820 + 870 = 336690
Step 388: 336690 + 870 = 337560
Step 389: 337560 + 870 = 338430
Step 390: 338430 + 870 = 339300
Step 391: 339300 + 870 = 340170
Step 392: 340170 + 870 = 341040
Step 393: 341040 + 870 = 341910
Step 394: 341910 + 870 = 342780
Step 395: 342780 + 870 = 343650
Step 396: 343650 + 870 = 344520
Step 397: 344520 + 870 = 345390
Step 398: 345390 + 870 = 346260
Step 399: 346260 + 870 = 347130
Step 400: 347130 + 870 = 348000
Step 401: 348000 + 870 = 348870
Step 402: 348870 + 870 = 349740
Step 403: 349740 + 870 = 350610
Step 404: 350610 + 870 = 351480
Step 405: 351480 + 870 = 352350
Step 406: 352350 + 870 = 353220
Step 407: 353220 + 870 = 354090
Step 408: 354090 + 870 = 354960
Step 409: 354960 + 870 = 355830
Step 410: 355830 + 870 = 356700
Step 411: 356700 + 870 = 357570
Step 412: 357570 + 870 = 358440
Step 413: 358440 + 870 = 359310
Step 414: 359310 + 870 = 360180
Step 415: 360180 + 870 = 361050
Step 416: 361050 + 870 = 361920
Step 417: 361920 + 870 = 362790
Step 418: 362790 + 870 = 363660
Step 419: 363660 + 870 = 364530
Step 420: 364530 + 870 = 365400
Step 421: 365400 + 870 = 366270
Step 422: 366270 + 870 = 367140
Step 423: 367140 + 870 = 368010

So, 870*423 = 368010